STAINS MAY be a blight on human existence, but it is in the act of staining, in fact, that terror lies.

Even as your hand first tips the brimming wine glass, alarms scream in your head. With adrenalin pulsing into your brain at an incredible rate, events unfold in horrible, dreamlike slowness. And you are powerless to change their course.

You funble for the glass, succeeding only in spraying it contents across the hostess' dress. And in that brief moment of spectacular clumsiness, you ask yourself: Why me? Why do I stain? Why am I here? (I don't even like these people.)

Hostesses beware. For like night creatures responding to the call of a full moon, stainers come out of the closets to stalk holiday season gatherings.

Over the years, Textile Museum experts Clarissa Palmai, fabric conservator, and Melissa Wood, a rug conservator who lectures there often, have heard the reports of numerous stain victims. Their strategies for stain removal are not magical. Their materials are downright ordinary.

But they give no guarantees. If the fabric or rug in question is one you treasure, and made of material delicate enough to be easily damaged, your best bet is taking it to a professional. ("The problem is," says Palmai, "there aren't very many good ones around.")

Keep on hand a standard ink blotter for fabrics and some white towels or rags for rugs. Also on the list of essentials is some neutral detergent (a detergent that doesn't lather too much and says "detergent" on the box), some mild bleach and an alkaline detergent, such as Borax or washing soda.

"One of the worst things," says Wood, "is to ignore a stain until it dries. Ignore it and you probably will end up with a stain." Wood, therefore, advocates blotting. Blot until it hurts. "If you do, you'll probably get most of it."

Urine: Of the stain litanies she hears, 75 to 80 percent of them, says Wood, are about pets watering carpeting. Her solution: "Get rid of the animal." Urine is chemically active and attacks fiber dyes. Be prepared to see some discoloring even if you get it out quickly. It can also rot cotton foundations.

After blotting as much of it out as possible, apply a neutralizing solution. A company in California markets an enzyme product called "Urine-Erase," designed specifically for pet problems. (It is available for $10 a pint from Ark Distributing Co., Inc., 2231-e Galaxy Court, Concord, Calif., 94520). If you can't get your hands on some fast, Wood recommends vinegar. Mix one pint with three pints of water.

Wine: Wine, as well as fruit juices, should be blotted out of carpets and fabrics as quickly as possible. Be sure to use white towels. Colors can otherwise bleach out of them and into the rug. Wood recommends using white vinegar to remove the remains from carpets. On fabrics, Palmai suggests neutral detergent and light bleaching.

Greasy Foods: Wood has found that baby powder or talcum powder will soak up grease on carpets and fabrics. After allowing it to sit, vacuum.

Coffee: Coffee and tea have both been used in the past as fabric dyes. Their ability to stain has been proved. After blotting either from the rug, use the suds from a neutral detergent to get out the rest. Fabrics with coffee spills should be rinsed out immediately in lukewarm water, says Palmai, then washed in a light cleaning solution.

Candle Wax: Candles may lend a warm tone to your holiday festivities, but you may be in for a shock when you turn up the lights later. To remove wax from fabrics, Palmai lays an ink blotter over the spot and irons the back of the blotter.

Blood: On fabrics stained with blood, use a "digester," a detergent with enzymes. If some remains, try a hot solution of alkaline detergent. Water Marks: Washing with a neutral detergent with some mild bleaching will help remove water marks. If they are stubborn, try spot bleaching with a Q-Tip.

The best solution of all, of course, is to be very careful about who you let in the house.